Currently, DRAM is the most common large-capacity semiconductor memory device and is widely used in computer systems. However, the DRAM is said to reach its miniaturization limit in a few years. Therefore, research and development of various large-capacity semiconductor memory devices has been conducted for the purpose of replacing the DRAM. Specifically, the following prior arts have been published on a thyristor and a floating body memory that stores a charge in a floating body of a bipolar transistor.
Patent Document 1 discloses a thyristor memory using a thyristor as a memory element. In Patent Document 1, a memory cell area is reduced by providing one access transistor and a plurality of thyristors connected in parallel with the access transistor. Further, in addition to the access transistor, a gate electrode that controls the turn-on/off of each of the plurality of thyristors is provided, and a word line is connected to each gate electrode. In other words, each thyristor is formed on a semiconductor substrate so as to function as a MOS transistor as well (refer to FIGS. 10, 12, and 14 of Patent Document 1).
Patent Document 2 discloses an FBC memory that uses a region immediately below a gate of a MOS transistor as a floating body. Patent Document 2 describes how an autonomous refresh is performed by the function of a bipolar transistor simultaneously driving a singular or a plurality of bit lines and a plurality of word lines in a data retention mode without using a sense amplifier.    [Patent Document 1]    Japanese Patent Kokai Publication No. JP-P2007-66364A    [Patent Document 2]    Japanese Patent Kokai Publication No. JP-P2009-176331A